Mask and method for forming the same

ABSTRACT

A photomask includes a low thermal expansion material (LTEM) substrate, a patterned opaque layer over the LTEM substrate, and a patterned capping layer over the opaque layer. The patterned capping layer includes a transition metal material for suppressing haze growth, such as metal oxide, metal nitride, or metal oxynitride. The material in the capping layer reacts with a hydrogenic compound from a lithography environment to for an atomic level hydrogen passivation layer. The passivation layer has superior ability to suppress photo-induced haze defect growth on the photomask surface, to improve production cycle time and reduce the production cost.

PRIORITY DATA

The present application is a divisional application of U.S. patentapplication Ser. No. 13/451,767, filed Apr. 20, 2012, which isincorporated herein by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed.

For example, the need to perform higher resolution lithography processesgrows. One method of many lithography techniques to improve resolutionis to use a super binary mask (BIM) or a phase shift mask (PSM). A phaseshift masks typically include an alternative phase shift mask (alt.PSM), and an attenuated phase shift mask (att. PSM). Disadvantages ofusing a phase shift mask are haze defects and haze related crystalgrowth defects on the photomask. Haze defects and haze related crystalgrowth defects on a photomask are photo-induced defects during highenergy expose, wave length ranging from 450 nm to 13 nm, such as 248 nmdeep ultraviolet (DUV) lithography process or 13 nm extreme ultraviolet(EUV) lithography process. The haze defects often require repeatedchemical cleaning processes to increase the IC production cycle time andcost. It is desired to have improvements for photomask haze defectsreduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with accompanying figures. It is emphasized that,in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposeonly. In fact, the dimension of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 represents a block diagram of a lithography system forimplementing one or more embodiments of the present invention.

FIG. 2 represents a flowchart illustrating a method of fabricating aphotomask according to various aspects of the present disclosure.

FIGS. 3-8 illustrate diagrammatic cross-sectional side views of anembodiment of a photomask at various stages of fabrication, according tothe method of FIG. 1.

DETAILED DESCRIPTION

The present disclosure relates generally to mask manufacturing andoptimization, and more particularly, to a method of suppressing haze orionic defect growth on photomask surface by modifying a capping layer ona photomask to form a self passivated hydrogenic layer, and thephotomask produced by such a method. The photomask includes a superbinary mask (BIM) or an alternative phase shift mask (alt. PSM) and anattenuated phase shift mask (att. PSM).

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Referring to FIG. 1, a photolithography system 100 is an example of asystem that can benefit from one or more embodiments of the presentinvention. The photolithography system 100 includes an illuminationsource 102, a plurality of illumination optics 104, a mask 106 (in thepresent disclose, the term mask, photomask, and reticle are used torefer to the same item), a plurality of projection optics 108 and atarget 110 such as a semiconductor wafer. However, other configurationsand inclusion or omission of devices may be possible. In the presentembodiment, the illumination source 102 includes a source providingelectromagnetic radiation having a wavelength range from UV to DUV. Forexample, mercury lamps provide UV wavelength, such as G-line (436 nm)and I-line (365 nm), and excimer lasers provide DUV wavelength, such as248 nm, 193 nm and 157 nm. The illumination optics 104 is configured toguide a radiation beam to the mask 106. The mask 106 may be a binary ora phase shift mask (PSM), which includes an alternative phase shift mask(alt. PSM) and an attenuated phase shift mask (att. PSM) as described infurther detail later below. The mask may be positioned on the reticlestage. The electromagnetic radiation beam reflected from the mask 106(e.g., a patterned radiation beam) is collected by the projection optics108. The projection optics 108 may be reflective and include amagnification lens for reducing the pattern image to be exposed on thetarget 110. The projection optics 108 also directs the patternedradiation to the target 110. The target 110 includes a photosensitivelayer (e.g., photoresist or resist), which is sensitive to the lightradiation. The target 108 may be held on a target substrate stage. Thetarget substrate stage provides control of the target substrate positionsuch that the image of the reticle is transferred onto the targetsubstrate in a repetitive fashion (though other lithography methods arepossible). The lithography system 100, or portions thereof, may includeadditional items, such as a vacuum system and/or a cooling system.

The photolithography system 100 may in a wet (immersion) or dryatmosphere environment. The photolithography surfaces, such as thesurface of the photomask 106, surface of the target 110, and/or surfaceof the optics 104, 108 are susceptible to defect and residue formation.Such defects may include haze, crystal growth, ionic residues, and oxideformation. Haze defect formation is especially problematic for advancedlithography technology that use a phase shift mask (PSM) such as analternative phase shift mask (alt. PSM) and an attenuated phase shiftmask (att. PSM), and short wavelength, high laser radiation energy.Photomask can be cleaned of haze defects by repeated wet chemicalcleaning and inspection. However, these processes increase the ICproduction cycle time the cost. As discussed in detail below, a cappinglayer is introduced on the photomask. In some embodiments, the materialsused in the capping layer react with ionic residue and then form aself-passivated hydrogen capping layer to suppress haze defect growth onthe photomask surface.

Referring now to FIG. 2, a method 200 can be used to fabricate a selfpassivated hydrogenic capping layer on the photomask 106 for haze defectgrowth suppression according to an embodiment of the present disclosure.Additional steps can be provided before, during, and after the method200, and some of the steps described can be replaced or eliminated forother embodiments of the method. Additionally, some steps may beperformed concurrently with other steps. The method begins at block 202,where an extremely low thermal expansion material is provided as asubstrate. At block 204, an opaque layer, a capping layer and a hardmask layer are sequentially deposited over the substrate to form a blankmask. At block 206, a suitable photoresist is deposited on the blankmask. The photoresist is patterned according to a design for a layer ofan integrated circuit (IC) device (or chip). At block 208, the hardmasklayer is selectively removed by an etch process, thereby exposing thetop surface of the capping layer. At block 110, the photoresist isstripped, thereby forming a hardmask pattern per the design. At block112, the capping and opaque layer is etched by using the patternedhardmask layer, thereby exposing a top surface of the substrate. Atblock 114, the fabrication of the self passivated hydrogenic cappinglayer photomask for haze defect growth suppression is completed. Anexample photomask produced by the method 200 is shown and described withreference to FIGS. 3-8.

FIG. 3 illustrates a blank mask 300 for fabricating the self passivatedhydrogenic capping layer photomask for haze defect growth suppression,such as would be produced at the end of step 204 (FIG. 2). The blankmask 300 includes a substrate 302. The substrate 302 may be made fromfused silica, fused quartz, calcium fluoride (CaF₂), silicon carbide,black diamond, silicon oxide-titanium oxide (SiO₂—TiO₂) alloy and/orother suitable low thermal expansion material (LTEM) known in the art. Ahigh degree of precision and purity on the surface and inside the bodyare desired when forming the substrate 302 because imperfections distortlight transmitted through and reflected off the finished mask.

The blank mask 300 further includes an opaque layer 304 deposited overthe LTEM substrate 302. The opaque layer 304 is formed such that anincident light beam will be fully absorbed by the deposited material. Inthe present embodiment, the opaque layer 304 includes a plurality ofmaterials, such as MoSi, TaON, TaN, and/or suitable materials. Theopaque layer 304 can be deposited on the low LTEM substrate 302 bysputter, chemical vapor deposition (CVD), physical vapor deposition(PVD), laser deposition, and/or atomic layer deposition (ALD).

Next, a capping layer 306 is deposited over the opaque layer 304. Thecapping layer 306 is formed such that it will react with ionic residueto produce self-forming efficiency surface modified layers to suppresshaze or ionic defect growth during and/or after a photolithographyprocess. In the present embodiment, the capping layer 306 includes aplurality of materials, such as metal oxide compounds (MOx), metalnitride compounds (MNx), or metal oxynitride compounds (MOxNy), whereexamples for M include Si, Ta, Ir, Ru, Hf, Os, or other transitionmetals. In the present, the crystalline state of the capping layer 306can range amorphous to a fine crystal structure. The capping layer 306can be deposited on opaque layer 304 by sputter, CVD, PVD, laserdeposition, ion beam sputtering, and/or ALD.

Next, the hardmask layer 308 is deposited over the capping layer 306.The hardmask layer 308 is a scarified layer, which can transfer apattern to the capping layer 306 and opaque layer 304 and can provideprotection from etchants attacking the capping layer 306 and/or theopaque layer 304 during an etch process. Example materials for thehardmask layer 308 include Cr, CrN, CrO, and CrON. The hardmask layer308 can be deposited over the capping layer 306 by sputter, CVD, PVD,laser deposition, and/or ALD.

Referring now to FIGS. 4-8, now that the mask blank 300 is performed asshown in FIG. 3, the mask is further processed to provide a selfpassivated hydrogenic capping layer and to form an atomic level hydrogenpassivation layer to suppress haze defect growth.

Referring to FIG. 4, a photoresist layer 402 is deposited over thehardmask layer 308 of the blank mask 300. The photoresist can bepositive or negative resist and can be deposited over hardmask layer 308using spin-on coating method per various coating tools.

Referring to FIG. 5, the photoresist layer 402 is patterned to form adesign layout. Typically the pattern is written on photoresist layer 402using a mask writing technique such as electron beam writing, ion beamwriting, or photolithography such as binary photolithography orphase-shift photolithography.

Referring to FIGS. 6 and 7, the patterned photoresist layer 402transfers the design layout pattern to hardmask layer 308 using a plasmaetching or wet etching process. The capping layer 306 is eitherresistant to the etch process, or includes an etch stop. A surface ofthe capping layer 306 is opened per the design layout after the etchprocess. The photo resist layer 402 can then be stripped by photoresiststripper, plasma or wet cleaning methods.

Referring to FIG. 8, the opened area capping layer 306 and theunderlying opaque layer 304 are removed by dry etching or wet etchingmethods to expose the underneath substrate layer 302 using the patternedhardmask 308. The etching stops at substrate layer 302. The patternedhardmask layer 308 is then stripped by a wet cleaning method to form thefinal mask with a patterned capping layer 306 and opaque layer 304 perthe design layout. Binary mask or phase shift masks used by thephotolithography system 100 (FIG. 1) can be fabricated according to thisembodiment.

When a conventional photomask is exposed to high energy radiationranging from 350 nm UV blue line to 13.5 nm EUV light, N is releasedfrom a Mo—Si substrate of the photomask, and the N reacts with H⁺ toform NH₄ ⁺ and NH₃, which attach to the Mo—Si oxidation surface. Theattached NH₄ ⁺ and NH₃ on the Mo—Si oxidation surface can then reactwith 50₄ ²⁻, which may be the residue from a cleaning process, to formhaze or ionic crystal growth defects. The binding energy between MoO₂and NH₄ ⁺ is higher than the binding energy between SiO₂ and NH₄ ⁺, andtherefore the haze defects are more easily grown in the optical absorberlayer than in the substrate region. The photomask discussed in thepresent disclosure prevents haze defects as discussed below.

In the present embodiment, an atomic level hydrogen passivation layerwill be formed on the mask surface during high energy exposure.Environment surplus hydrogen or hydrogen functional ions such as fromNH₄ ⁺ or NH₃, will form and the surface will absorb these hydrogen ionsas surface passivation reaction. The mechanism can be as below:

H⁺+NH₄ ⁺→contact radical ion pair+NH₃(g)+H₂(g)

For example, assuming the capping layer 306 of the photomask comprisesTaN or TaO, the chemical reactions in this embodiment can be describedas below:

NH₄ ⁺+TaO(surface)+hv→TaO:H(surface passivation)+NH₃(g)

NH₄ ⁺+TaN(surface)+hv→TaN:H(surface passivation)+NH₃(g)

Once hydrogen is terminated in the absorber surface, dangling bonddensity and surface energy can be decreased, and therefore, ioninteraction activity can be suppressed.

Thus, the present disclosure describes a unique photomask, such as aphase shift mask. In one embodiment, the photomask includes a lowthermal expansion material (LTEM) substrate, a patterned opaque layerover the LTEM substrate, and a patterned capping layer over the opaquelayer. The patterned capping layer includes a transition metal materialfor suppressing haze growth. Examples of the capping layer include metaloxide, metal nitride, and metal oxynitride.

The present disclosure also describes a unique method for makingphotomask. In one embodiment, the method of preparing a photomaskincludes depositing an opaque layer on a low thermal expansion material(LTEM) substrate and depositing a capping layer on the opaque layer. Thecapping layer includes a material for suppressing haze growth on asurface of the photomask. The method also includes depositing ascarified hardmask layer on the capping layer, patterning the scarifiedhardmask layer, and patterning the capping layer and opaque layer usingthe patterned scarified hardmask layer.

In another embodiment, a method of forming a photomask includesdepositing an opaque layer above a low thermal expansion material (LTEM)substrate, depositing a capping layer above the opaque layer, anddepositing a hardmask layer above the capping layer. The hard mask layeris patterned by a lithography and etching process. The method furtherincludes patterning the capping and opaque layers using the patternedhardmask and a first etch and strip process and removing the patternedhardmask using a second etch process. The capping layer is made of amaterial which reacts with a hydrogenic compound that exists in alithographic environment and thereby forms hydrogenic bonding on thecapping layer surface.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of preparing a photomask, comprising: depositing an opaque layer on a low thermal expansion material (LTEM) substrate; depositing a capping layer on the opaque layer, wherein the capping layer includes a material for suppressing haze growth on a surface of the photomask; depositing a scarified hardmask layer on the capping layer; patterning the scarified hardmask layer; and patterning the capping layer and opaque layer using the patterned scarified hardmask layer.
 2. The method according to claim 1, wherein the opaque layer includes MoSi, TaON, TaN, or combinations thereof, and is deposited on the LTEM substrate by one of a sputter deposition, a chemical vapor deposition (CVD), a physical vapor deposition (PVD), a laser deposition, and an atomic layer deposition (ALD) process.
 3. The method according to claim 1, wherein the capping layer includes a metal oxide compound, wherein the metal oxide compound includes Si, Ta, Ir, Ru, Hf, Os, or other transition metal, and is deposited on the opaque layer by one of a sputter deposition, a chemical vapor deposition (CVD), a physical vapor deposition (PVD), a laser deposition, and an atomic layer deposition (ALD) process.
 4. The method according to claim 1, wherein the capping layer includes a metal nitride compound, wherein the metal nitride compound includes Si, Ta, Ir, Ru, Hf, Os, or other transition metal, and is deposited on the opaque layer by one of a sputter deposition, a chemical vapor deposition (CVD), a physical vapor deposition (PVD), a laser deposition, and an atomic layer deposition (ALD) process.
 5. The method according to claim 1, wherein the capping layer includes a metal oxynitride compound, wherein the metal oxynitride compound includes Si, Ta, Ir, Ru, Hf, Os, or other transition metal, and is deposited on the opaque layer by one of a sputter deposition, a chemical vapor deposition (CVD), a physical vapor deposition (PVD), a laser deposition, and an atomic layer deposition (ALD) process.
 6. The method according to claim 1, wherein the scarified hardmask layer includes Cr, CrN, CrO, CrON, or combinations thereof, and is deposited on the opaque layer by one of a sputter deposition, a chemical vapor deposition (CVD), a physical vapor deposition (PVD), a laser deposition, and an atomic layer deposition (ALD) process.
 7. The method according to claim 1, wherein the scarified hardmask layer is patterned using a mask writing technique.
 8. The method according to claim 1, wherein patterning the capping layer and opaque layer includes etching using the patterned scarified hardmask with an etchant that is selective to the capping layer and opaque layer, and thereafter stripping the patterned scarified hardmask with an etchant that is not selective to the capping layer and opaque layer.
 9. A method comprising: receiving a low thermal expansion material (LTEM) substrate; forming a patterned opaque layer directly coupled to the LTEM substrate; and forming a patterned capping layer directly coupled to the patterned opaque layer, wherein the patterned capping layer includes a material for suppressing haze growth.
 10. The method of claim 9, wherein the LTEM substrate includes one or more selected from the group consisting of quartz, silicon, silicon carbide, calcium fluoride (CaF2), and silicon oxide-titanium oxide alloy (SiO2-TiO2).
 11. The method of claim 9, wherein the patterned opaque layer includes one or more selected from the group consisting of MoSi, TaON, and TaN.
 12. The method of claim 9, wherein the patterned capping layer includes an oxide compound, the oxide compound including one selected from the group consisting of Si, Ta, Ir, Ru, Hf, and Os.
 13. The method of claim 9, wherein the patterned capping layer includes a nitride compound, the nitride compound including one selected from the group consisting of Si, Ta, Ir, Ru, Hf, and Os.
 14. The method of claim 9, wherein the patterned capping layer includes an oxynitride compound, the oxynitride compound including one selected from the group consisting of Si, Ta, Ir, Ru, Hf, and Os.
 15. The method of claim 9, wherein the patterned capping layer includes a crystalline state between amorphous and fine crystal, inclusive.
 16. The method of claim 9, wherein the patterned capping layer is configured to react with ionic residue and thereafter form a self-passivated hydrogen capping layer to suppress haze or ionic defect growth on a photomask surface during or after a deep ultraviolet (DUV) or extreme ultraviolet (EUV) lithography process.
 17. The method of claim 9, wherein the photomask is one of a binary mask and a phase shift mask.
 18. The method of claim 9, wherein the photomask includes a binary mask, an alternative phase shift mask (alt. PSM) portion, or an attenuated phase shift mask (att. PSM) portion.
 19. A method of preparing a photomask for suppressing haze growth, comprising: depositing a patterned opaque layer directly over a low thermal expansion material (LTEM) substrate; and depositing a patterned capping layer directly over the patterned opaque layer.
 20. The method of claim 19, wherein the patterned capping layer includes a transition metal material for suppressing haze growth. 